A Group III nitride semiconductor can cover a wide range of band gaps by changing the composition of Ga, Al, In, and the like, which are Group III elements, and therefore is widely applied to optical semiconductor devices, such as an LED (light emitting diode) and an LD (semiconductor laser), electronic devices for high frequency and high output power purposes. In general, the devices are produced by epitaxially growing a Group III nitride crystal on a sapphire substrate.
However, the lattice mismatch ratio between a sapphire substrate and a GaN crystal, which is a Group III nitride semiconductor, (((lattice constant of GaN)−(lattice constant of sapphire))/(lattice constant of GaN)) is 13.8%, and thus the Group III nitride crystal thus epitaxially grown has a large defect density. Accordingly, there has been a problem that the characteristics of the device using the Group III nitride semiconductor are restricted.
In view of the problem, for reducing the defect density of the Group III nitride crystal, there has been a proposal of a technique of epitaxially growing GaN on a substrate formed of ScAlMgO4 (Patent Literature 1). The lattice mismatch ratio between ScAlMgO4 and GaN (((lattice constant of GaN)−(lattice constant of ScAlMgO4))/(lattice constant of GaN)) is as small as −1.8%. Under the circumstances, there is an expectation of application to various devices of a Group III nitride semiconductor that uses a single crystal represented by RAMO4 (wherein R represents one or a plurality of trivalent elements selected from the group consisting of Sc, In, Y, and a lanthanoid element, A represents one or a plurality of trivalent elements selected from the group consisting of Fe(III), Ga, and Al, and M represents one or a plurality of divalent elements selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd) (which may be hereinafter referred to as an “RAMO4 substrate”), examples of which include ScAlMgO4, as a substrate for epitaxial growth of a Group III nitride crystal.
Patent Literature 1: JP-A-2015-178448